AoPS Wiki talk:Problem of the Day/September 5, 2011
Revision as of 07:28, 7 September 2011 by Negativebplusorminus (talk | contribs)
Problem
Simplify ![\[2(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}+\cdots)\]](http://latex.artofproblemsolving.com/8/2/9/829bf38e0288e849f8d4b0fe988cce6f5fb00053.png)
Solution
The series
![\[1+\frac{1}{2}+\frac{1}{4}+\cdots\]](http://latex.artofproblemsolving.com/2/1/5/2157cad0cf38e290384bbdeecd3d7f8b3427b3f7.png)
is a geometric series, which famously converges to 2. This can by applying the formula for infinite geometric sums, 
where 
is the first term and 
is the ratio. For this series, the sum is 
. Thus, since the problem asks for twice this number, the answer is 
.
